| Tecken | Tl |
| Atomnummer | 81 |
| Grupp | 13 (Borgruppen) |
| Period | 6 |
| Block | p |
| Ämnesklass | Övrig metall |
| Utseende | Silvery white |
| Färg | Silver |
| Antal protoner | 81 p+ |
| Antal neutroner | 123 n0 |
| Antal elektroner | 81 e- |
| Fas vid STP | Fast |
| Densitet | 11.85 g/cm3 |
| Relativ atommassa | 204.382 u |
| Smältpunkt | 577 K 303.85 °C 578.93 °F |
| Kokpunkt | 1746 K 1472.85 °C 2683.13 °F |
| Ångbildningsvärme | 162.09 kJ/mol |
| Elektronegativitet (Paulingskalan) | 1.62 |
| Elektronaffinitet | 36.4 kJ/mol |
| Oxidationstal | −5, −2, −1, +1, +2, +3 (a mildly basic oxide) |
| Jonisationspotential |
|
| Upptäckt | William Crookes (1861) |
| Första isolation | Claude-Auguste Lamy (1862) |
Upptäckten av tallium Thallium (Greek θαλλός, thallos, meaning "a green shoot or twig") was discovered by William Crookes and Claude Auguste Lamy, working independently, both using flame spectroscopy (Crookes was first to publish his findings, on March 30, 1861). The name comes from thallium's bright green spectral emission lines. As both scientists discovered thallium independently and a large part of the work, especially the isolation of the metallic thallium was done by Lamy, Crookes tried to secure his own priority on the work. Lamy was awarded a medal at the International Exhibition in London 1862: For the discovery of a new and abundant source of thallium and after heavy protest Crookes also received a medal: thallium, for the discovery of the new element. | |